When a toilet does not flush completely, the cause may be a clog in the toilet's drain line from waste or toilet paper creating a block in the drain. Another possibility for the toilet not flushing properly is hard water deposits accumulating in the toilet bowl's ports, clogging them enough that the water does not enter the bowl with enough force. Using a bucket of water, you can determine the cause of the toilet's sluggish flushing.
Pour a bucket of water into the toilet bowl as quickly as you can, without the water sloshing over the edge of the bowl and onto the bathroom floor. If the toilet flushes normally, then the problem has to do with buildup in the port passageways between the toilet's tank and the bowl. If the toilet does not flush normally, then the problem is a clog in the drain line.
Press a plunger's cup over the drain opening in the toilet bowl if there is a clog in the drain line. Push and pull the plunger's handle up and down, while keeping the cup covering the drain hole, working to dislodge the clog in the drain line.
Feed a toilet snake into the drain opening if the clog in the drain line does not come free with the plunger. Feed the drain snake down the drain line until you feel it contact the clog, then turn the snake's handle clockwise to bore through the clog. Turn the handle counterclockwise as you pull the toilet snake out of the drain.
Clean out the port holes, located under the rim of the toilet bowl, with a wood skewer to remove any buildup left in the port holes. Open a window in the bathroom and put on a respirator before pouring a mixture of one part muriatic acid with 10 parts water down the overflow tube inside the toilet's tank.
Flush the toilet once after you let the solution sit in the toilet for half an hour. If the toilet still flushes sluggishly, pour more solution down the overflow tube and wait another half hour before flushing again.